I could use some help in properly discribing the purpose of Bonding.

I would like to add a comment in my remarks section of my report about bonding.

In the report I have an area where I check if there is a bond across the hot water tank. As of today I have no remarks for my clients to understand.

Can any of you come up with a 1-3 line statement pertaining to bonding.

This is what I have so far.

Bonding is connecting any mettallic piping that may become energized must be bonded (to ground) Often heaters are installed with dielectric unions which breaks any grounding path thru the heater.

Thank you for your time


Now…you knew I would have some comments on that…lol

To be honest your statement is rather fine in that you have to draw a fine line between giving the client too much information they begin to lose the actual meaning of the statement.

To be honest with you the best definition I can think of is the one in the NEC handbook.

“The purpose of bonding is to establish an effective path for fault current that, in turn, faciliates the operation of the overcurrent portection device. The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likeley to be imposed on it.”

Well I kinda broke it into a entire speal…but basically covers the 2 fold meaning of the Bonding process in as fast a terms possible while still giving the defined function of it, I would probably not go into specific items and simply add the definition listed above on bonding to the form with a icon displacing it in case they need to refer to the definition.

hmm…Ok…generic one liner

“The purpose of bonding is to establish an effective path for fault current that, in turn, faciliates the operation of the overcurrent portection device.”

Well one line if you use a LONG piece of paper…thehehe

One liner for most homeowners to understand…

" The metal wire thingie that connects all other exposed metal thingies back to the wall thingie that help big box on the wall thingie and its little switch thingies shut off if I use too much of the stuff coming out of the doo hickie or when I stick a fork in the wall whicha-ma-call-it"

Not sure you should use this one…I think it is a little too long.


While we are on the subject of bonding, inspecting a 600 AMP. service panel this morning for a commercial building built in 1965 with the electrical updated in 1985, what size conductor would be allowable to terminate to the metallic sprinkler system.



The size of the GEC is determined by the size of the largest ungrounded service-entrance conductor, not the disconnect rating.

If the SEC is 600 kcmil to 1100 kcmil copper or 900 kcmil AL through 1750 kcmil AL, the min size of the GEC is required to be 2/0 copper or 4/0 AL


The service conductors are not visible (panel locked, another issue), and I cannot determine an exact grounding location either but there is a 1/0 copper conductor terminated to the sprinkler piping, which I knew would be to small.

I have to go back tomorrow, after the Realtor reflects upon my notice to make sure everything is unlocked…Realtors.:shock:

My electrician is on vacation or I would have had him cut the lock.


Dave Paul has certainly given some good suggestions I only want to add is that we are not really bonding these items to earth so much as bonding them all to the neutral/grounding bar of the service panel.

It is this connection to the neutral that creates the reliable low impedance fault path needed to open the breakers or fuses.

The connection to earth is somewhat incidental due to the grounding electrodes.

The grounding electrodes serve little purpose for the voltages normally running around a home.

Grounding electrodes come into play for lighting strikes and power company faults that can send very high voltage into the home wiring.

When you say “bond across the hot water tank…” are you thinking about the water lines, if so I believe that the following may also be considered in your case, because it is “**[FONT=Courier New]Other Metal Piping”[/FONT]**installed in or attached to a building or structure, and the metal piping system(s), including gas piping, that is likely to become energized is required to be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used …

I would also use this statement to give a reason to your clients:

FPN: Bonding all piping and metal air ducts within the premises will provide additional safety.

PS: See the NACHI glossary when you are in need of some explanation:


Sorry I had a service call to run to…back to your question.

Is the system you are talking about the internal fire sprinkler system on the commercial building itself?

Their are two articles that could apply here if twisted in different ways…250.66 and 250.122…now some will argue either way and I can present to you WHY it could very possibly be either chart depending on the setup.

Is their more information you can give me about this service…it is 600A so is it (3) 3/0 CU parallels…meaning 3 phase…or what.

I can spit out a number for you but it is better to present all the info and explain why I have come up with the size…it can be spun many ways…

Most will spit out 250.66 right away…and base it on the size of the largest ungrounded conductor and their is a OR in that statement when sizing in that chart…but their is a few specific areas that could spin you over to 250.122 as well…

Before I give reason to why you rule one out...I need to know a little more on the system.

1.) Is it a common service to ONLY the one building, does it feed any other buildings from this service location.

2.) What are the size conductors…I have a hard time thinking they would have run something larger than a 600 KcMil and such…so chances are it is parallel 3/0 CU…but I could be wrong.

3.) Is their anything on this sprinkler system " other piping " that can become or likely to become energized as well based on your observation…and is the system powered at the source of the controller from anything that has a dedicated circuit to it.

We don’t usually specifically bond sprinkler systems here.

The sections that are likely to become energized end up grounded / bonded through the EGC of the very equipment that could energize it. Fire pumps, jokey pumps, pressure or flow switches etc.

In no case would it need to be sized per 250.66, 250.122 is the the table to use.

Paul, I could not get into the panel it was locked, my electrician will not be back till tomorrow. (with bolt cutters)

This is just a free standing woodworking shop. 600 Amp three phase four wire.

The metallic sprinkler piping is in the wall coming out of the ground with what appears to be a 1/0 copper conductor attached with a bonding strap. I can only see a small portion where the electrical system is bonded or ?grounded? below the shutoff valve.

Since you were on the bonding subject when I was looking at the board I thought you might be able to guess what size conductor would be allowable without knowing the service conductor size.


Pardon my ignorance here :roll: , but why would 250.122 be used in this case rather than 250.66?

250.122 is for sizing of equipment grounding conductors (EGC’s) and 250.66 is for sizing of grounding electrode conductors (GEC’s).

If we’re referring to service equipment, would we not be talking about the GEC? Load side equipment and panels would be where we look for EGC’s, no?

Yeah your ignorant like I am skinny :slight_smile:

When bonding Metal Water Piping 250.104(A) requires us to use 250.66

When bonding “Other Metal Piping” ducts, gas lines, sprinkler pipes, compressed airlines etc. 250.104(B) allows us to use 250.122

It gets pretty involved as to why but to keep it short the Other Metal Piping only needs a bond wire equal to the EGC of the equipment that may energize it.

ok…You know someone wiser than me just told me to keep it simple and you know…I have GREAT respect for that person so I will cut to the chase as I was possibly going to do a lesson here but should just cut to the chase as bob eluded to and save MANY brain cells from being crisp at the end of the day…

Due to Section 250.104(B) the sprinker system would be covered under 250.122.

Jeff " The Zinsco" Pope…my friend you are not alone here which is why I was going to elaborate on it more but I really should not as it can get confusing…the sprinker system is not considered anything to do with the water pipe grounding electrode or anything…it as Bob put GREATLY…not even bonded in many AHJ locations…

But it is indeed refered to under 250.104(B) you will see where it refers to 250.122 as the size required…

That is why I was going to post some weird examples but again is really outside of the scope of an HI…now if any electrical junkies want to e-mail me we can get down into the nitty gritty…lol…Not you BOB…I can’t teach you anything you do not already know fella…lol

The point is you can NEVER be sure if something will become energized, Mike holt tells about a story where a rat ate threw a wire and it contacted a gas metal pipe that no one ever thought would be energized…well guess what it killed a kitchen worker…so assuming could KILL ya…

Dang you bob…thehehe…Could have saved me all the typing.

lol…Translation : If the sprinkler system is run to a manafold that has lets say a 30A circuit ( being hypothetical here I have no idea what size feeds the fire protection device relays…hmmmm did I spell that right…? ) then you could directly bond the pipe at that location with a # 10 AWG CU wire and meet the requirements of 250.104(b)

I thought we were talking about the 600 amp service equipment #-o

That’s what I get for buying into the thread drift. . .

Doing commercial inspections without a licensed electrician is like…:shock:

There are wayyyyyyy to many what if could be’s. As we all know.

But I do find your posts very interesting…:smiley:

Thanks, Guys

I’d like to go back to the one-liner to explain what bonding is.

Any more ideas?

What does bonding do?

Does it prevent one from getting shocked to death if there is a short in an appliance?
Does it prevent one from getting shocked to death if there is a short in the wiring?
Does it prevent fires?

I think if we can answer what it does without using the technical terms, then we can create a one-liner stating what it is.

I have a two-liner in my report:

Quite frankly, I wrote that four years ago when my knowledge of bonding was much less than it is now, so I don’t know if it is technically correct. However, along with the attached picture, and my use of the words “electrical grounding,” I’ve never had a Client not understand (perhaps not technically, though) what was going on or what needed to be done.

And the plumber and/or electrician also has always understood. And I’ve gotten no derogatory calls from anyone.

Water heater bonding jumper 01.jpg